Mid and Deep Circulation in the Japan Sea

日本海是一个小型海洋，是海洋数值预报的一个很好的试验盆。然而，到目前为止，人们对中深环流的认识还不是很清楚。作为日本、韩国、俄罗斯的国际合作实地考察，我们在1994、1995两个会计年度进行了4次表层以下环流调查。在日本海主要海域（1994年，7.5-7.25）夏季巡航期间的CTD和化学测量表明，深层温度以每10年0.02 C的速率升高，而氧气减少，表明至少在最近10年没有形成深水。通过对日本盆地深部恢复的长期（1993.8 ~ 1994.8）系泊资料的分析，发现了强烈的月尺度、速度超过20 cm/s的中尺度活动。在这次巡航中获得了许多关于盐度最小层与氧气最大值分布的信息。1996年冬季在符拉迪沃斯托克附近进行的第二次冬季巡航（1996.2.15-2.25）探测到深度达600m的深对流，而第一次冬季巡航（1995.3.1-3.15）由于1995年冬季较为温暖，没有发现深对流的迹象。夏季航行期间（1995.5.26-6.8）在若浅湾附近进行的ADCP和CTD测量观测到对马流近岸分支下的次表层逆流在大陆架断裂带上，速度超过10 cm/s。这种暗流的存在和结构与几个数值模型的结果吻合得很好。本研究发现了许多关于中深层环流的新方面，将对今后对日本海环流的研究有很大的帮助。

The Japan Sea is a mini ocean and a very good test basin for the numerical ocean prediction. However, so far, the intermediate and deep circulation haven't been well understood. We carried out 4 cruises to survey the circulation below the surface layr during two fiscal years (1994,1995) as international cooperative field researches between Japan, Korea nad Russia.The CTD and chemistry measurements during the summer cruise in the main part of the Japan Sea (1994,7.5-7.25) showed the increase of the temperature in the deep layr with the rate of 0.02 C per 10 years and the oxgen decrease, suggesting no formation of the deep water during at least last ten years. Strong mesoscale activities with the time scale of month and the velocity exceeding 20 cm/s were detected in the deep Japan Basin by analyzing the recovered long-term (1993.8-1994.8) current mooring data. Many informations about the distribution of the salinity minimum layr with the oxgen maximum were obtained in this cruise.The second winter cruise (1996.2.15-2.25) carried out off Vladivostok in '96 winter detected the deep convection reaching 600m depth, while no sign of deep convection could be found in the first winter cruise (1995.3.1-3.15), because the winter in 1995 was warm.The ADCP and CTD measurements carried out during the summer cruise off the wakasa bay (1995.5.26-6.8) observed the subsurface counter current below the nearshore branch of the Tsushima current over the continental shelf break with the speed exceeding 10 cm/s. The presence and the structure of this undercurrent correspond well to the results of several numerical models.Many new aspects about the intermediate and deep clrculation found in this research will contribute much to the future studies for the Japan Sea circulation.